kinetic energy

kinetic energy

by Matthew Everest

Multiple Choice

What is the change in kinetic energy of a 10kg toy starting at rest and accelerating to 2m/s?

• 40J

• 20J

• -20J

• -40J

​energy can be measured in different units

Multiple Choice

How many joules of energy is there in a big mac of 540 calories? (see conversion on previous slide)

• 2.26 J

• 2.26 million joules

• 2226 joules

• 226J

​Kinetic Energy is a scalar (has no direction)

• ​No types of Energy have a direction so all are scalars.

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• Any one object cannot have negative kinetic energy.

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• ​The lowest value an object can have is 0 if it is not moving.

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• ​Remember if a number has a direction it is a vector

Fill in the Blank

Kinetic energy is not a ______ quantity because it has no direction directly linked.

​kinetic energy in more than one dimension

• ​If an object is moving through a 3 dimensional space then we can split the velocities into x ,y and z components.

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​v_z is how much of the velocity is in the z direction

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​v_y is how much of the velocity is in the y direction

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​v_{x is how much of the velocity is in the x direction}

​The kinetic energy equation in 3 Dimensions.

​Example

​A 0.4kg football is corner kicked. The ball iniailly moves up with a v_y = 7m/s, it moves forwards towards the goal with a v_z = 12m/s, and It curls to the left with v_x = 1m/s. What is the total kinetic energy of the ball?

Multiple Choice

The velocity of a boat moving across the water in the x direction is 8 m/s. The boat also moves at 3m/s in the z direction at the same time. What is the total kinetic energy of the boat if it has a mass of 40000kg? (remember 1 MJ = 1000000J)

• 1.152J

• 1.46MJ

• 1152000J

• 1152MJ

Multiple Choice

The boat from the previous question was moving in how many dimensions?

• 1

• 2

• 3

• 4

​Work done , W

Multiple Choice

Find the mass of a ball that speeds up t 5m/s speed from rest after 100J of work is done on the ball.

• 1.1kg

• 1.4kg

• 8.6kg

• 2.8kg

Multiple Choice

The work done on an object is equal to the change in kinetic energy. How much work is done on a 2000kg car to accelerate it from rest to 20m/s?

• 4000J

• 40J

• 400000J

• 4J

Multiple Choice

The work done on an object is equal to the change in kinetic energy. How much work is done by the brakes on a 2000kg car to slow it down to stop it?

(work done can be minus)

• -400000J

• -4000J

• 400000J

• 20000J